Chemical Mechanical Polishing or Chemical Mechanical Planarization (CMP) is a process used to manufacture semiconductor wafers. CMP uses an abrasive and corrosive chemical slurry (commonly a colloid) in conjunction with a polishing pad and retaining ring, typically of a greater diameter than the wafer. The pad and wafer are pressed together by a dynamic polishing head and held in place by the retaining ring. The dynamic polishing head is rotated with different axes of rotation (i.e., not concentric). This action removes material and tends to even out any irregular topography, making the wafer essentially flat (or planar).
Polish time is generally an important CMP parameter which is based on the estimate of a planar end-point. However, conventional CMP control methods do not accurately account for multiple tool and process parameters such as film type, tool differences, new devices, and consumable changes over their life. Specifically, the polish rate is known to change with consumable life (e.g., pad life), is non-linear, and varies with the tool. This affects chart targeting and centering (CPk).
For example, for dielectric CMP, each dielectric (e.g., oxide) film change on the tool requires qualification of the CMP tool by first running a pilot (unpatterned) wafer with the particular dielectric to be polished thereon. Pilot wafers increase the cycle time (CT) and result in increased cost. Moreover, every new product device requires a look-ahead wafer to set the device specific polish rate which is known to vary based on the pattern density on the particular device. This affects both CT and cost. Although some polish time prediction equations are known, such known polish time prediction equations do not include a post CMP target, which can cause confusion when setting up new CMP process flows.